1. Field of the Invention
The present invention relates to aluminum nitride sintered bodies and members for semiconductor-producing apparatuses using the same.
2. Description of the Related Art
Materials mainly composed of aluminum nitride are applied for electrostatic chucks, heaters for producing semiconductors and the like. When a sintering aid such as a rare earth metal oxide or an alkaline earth metal oxide is added to a raw material powder of aluminum nitride, the sintering aid reacts with oxygen impurity (alumina) on the surface of the aluminum nitride powder to form a liquid phase consisting of rare earth metal-Alxe2x80x94O or alkaline earth metal-Alxe2x80x94O, so compacting and grain growing of the powder are promoted. Concurrently, a trap effect of the oxygen impurity by rare earth metal oxide or alkaline earth metal oxide inhibits oxygen dissolution into the aluminum nitride to achieve a high thermal conductivity of the sintered body.
For instance, NGK Insulator, Ltd. disclosed in JP-A 9-315,867 that the volume resistivity of the aluminum nitride sintered body with high purity could be controlled to 108 to 1012 xcexa9xc2x7cm at room temperature by adding a very small amount of yttrium oxide thereto.
JP-B 63-046,032 discloses a process for producing an aluminum nitride sintered body having a high thermal conductivity. According to the claim, aluminum nitride powder containing 1 wt. % of oxygen is mixed with 0.01 to 15 wt. % of the oxide of metal element selected among yttrium, lanthanum, praseodymium, niobium, samarium, gadolinium and dysprosium to obtain mixed powder. The powder is then shaped and sintered to obtain an aluminum nitride sintered body having a high thermal conductivity and containing 0.01 to 20 wt. % of oxygen. In Example 1 in this patent specification, a sintered body having a thermal conductivity of 121 W/mxc2x7K at room temperature is acquired by adding 3 wt. % of a samarium oxide powder to an aluminum nitride powder containing 1 wt. % of oxygen (average particle diameter=1 xcexcm), mixing the resultant powder and hot-pressing the mixture at 1800xc2x0 C. under a pressure of 300 kg/cm2 for one hour.
Since a semiconductor-producing process such as a CVD process or a sputtering process needs to form a semiconductor on a wafer, it is generally necessary to heat the wafer to a high temperature range of at least 100xc2x0 C., particularly at least 200xc2x0 C. In this occasion, an attracting face of an electrostatic chuck is heated by a heater buried in the electrostatic chuck or a heater so placed that it may contact with the electrostatic chuck below the electrostatic chuck.
In the electrostatic chuck, the temperature of the wafer is low at the time of placing the wafer on the attracting face of the electrostatic chuck. The temperature increases to a saturation temperature after the wafer is attracted to the chuck. In such an electrostatic chuck and a semiconductor-producing apparatus, aluminum nitride grains may be peeled and become particles due to an impact upon the wafer contacting with the electrostatic chuck immediately after the wafer is attracted, and due to a deformation of the wafer caused by a thermal expansion after the contact.
An object of the present invention is to provide aluminum nitride sintered bodies which hardly peel aluminum nitride grains and exhibit high resistivity of at least 108 xcexa9xc2x7cm even in a high temperature range of, for example, 300-500xc2x0 C., as well as relatively high thermal conductivities.
Another object of the present invention is to provide members for semiconductor-producing apparatuses which hardly peel aluminum nitride grains in the semiconductor-producing apparatuses and exhibit high resistivity of at least 108 xcexa9xc2x7cm even in a high temperature range of, for example, 300-500xc2x0 C., as well as relatively high thermal conductivities by using such aluminum nitride sintered bodies.
The present invention relates to aluminum nitride sintered bodies containing aluminum nitride as a main component, at least one rare earth metal element in an amount of not less than 0.4 mol % and not more than 2.0 mol % as calculated in the form of an oxide thereof and aluminum oxide component in a amount of not less than 0.5 mol % and not more than 2.0 mol %, wherein Si content is not more than 80 ppm and an average particle diameter of aluminum nitride grains is not more than 3 xcexcm.
The present invention also relates to members for semiconductor-producing apparatuses wherein at least a part of the members comprises the aforementioned sintered bodies.